1. Field of the Invention
The present invention relates to a charging apparatus, and is more specifically to a charging apparatus that is capable of charging with a relatively small charging current.
2. Description of Related Art
In a charging apparatus for charging a secondary battery such as a nickel metal hydride battery or the like, it is typical to use, for example, a charging control timer in order to end charging operation at a predetermined constant time period after the start of charging operation (see Japanese Patent Application Publication No. S63-194533). Alternatively, charging may be terminated based on the judgment that the full charging is reached by detecting such phenomena as a minus delta V value (−ΔV detection) in voltage of the secondary battery which is being charged, a gradient of temperature rise of the battery (dT/dt detection), the upper limit of the temperature rise of the battery (TCO detection), and the like during the charging.
However, in case of terminating the charging after a predetermined constant time period is passed, if the secondary battery is recharged after use or interruption of the charging operation of such battery, the charging control timer is reset regardless of the amount of the battery capacity of the secondary battery decreased by discharging, thereby carrying out the charging operation again for the same predetermined constant time period from the new start of the charging operation before termination.
The constant charging time period is normally set to the time which is sufficient for charging a secondary battery, which has been discharged to the final discharge voltage, back to its rated capacity.
Accordingly, if the charging operation is repeated by starting the whole charging operation before discharging to the final discharge voltage, the battery may be overcharged, thereby causing inconvenience that may lead to degradation in performance of the secondary battery.
Japanese Patent Application Publication No. S63-194533 also discloses a technology which does not to reset the timer in case of short break of the AC power supply or the like during the charging operation of the secondary battery, but the timer is reset when the secondary battery is removed from the charger.